In recent years, there has been a rapid proliferation of mobile phones. In some cases, a single person owns a plurality of mobile phones. Further, mobile phones are not only carried by persons. It has also been considered to attach a chip having a communication function to a pet, or to install a communication function in a machine apparatus or the like, to carry out communication with the pet or the machine apparatus. In this manner, when it becomes possible to manage anything including persons, pets, apparatuses and the like via a mobile communication network, for example, it also becomes also possible to monitor the location of persons, pets, apparatuses and the like.
Here, various methods for monitoring the location of mobile phones and the like have been considered. For example, a GPS apparatus is installed in a mobile phone or the like to manage the location of the mobile phone or the like by using GPS information. For example, Non Patent Literature 1 discloses a positioning system by which latitude, longitude, and altitude information is obtained by performing triangulation on the ground using radio waves from a satellite. Further, a mobile phone or the like is connected to a nearby base station when using a mobile communication network. Base stations are generally arranged at intervals of from several hundred meters to several kilometers. Accordingly, by specifying a base station with which a mobile phone communicates, i.e., a base station to which a mobile phone is connected, the rough location of the mobile phone can be specified. For example, Non Patent Literature 2 discloses measuring the direction of a mobile phone at a plurality of base stations, and deriving the location of the mobile phone from the measured directions.